I'm rather astonished they get away with such tiny relays, even if it is never "hot switched".
At high impedances there can be thousands of volts of RF in there, even at the moderate power levels it's specified for. In my experience that sort of voltage easily produces coronas that would put a smile on Tesla's face. I'm used to seeing several inches of ceramic insulation or air space between conductors at those power levels. (Most of us O.T.s raised with vacuum tubes have pulled inches long arcs off of the high-impedance tank circuit of our rigs at far less than 200 watts.) At very low impedances the currents can run into correspondingly huge amounts, with substantial ohmic losses in the inductor wires and relay contacts. I'm used to seeing tubing or at least large gage wire used for inductors to minimize that problem. Sometimes the wires are silver plated. Even heavy-duty commercial automatic tuners, such as those used on ships for the HF rigs, have very specific combinations of minimum length of antenna and minimum frequency they can handle because it's an electrically-short antenna that produces the highest voltages. Since Stewart found that losses escalate at impedance extremes, maybe they aren't getting away with using those tiny relays or the little inductors. Ron AC7AC -----Original Message----- I made a carbon copy of this ATU. It works pretty well, however at impedance extremes it was a bit lossy. Stewart G3RXQ >> > Here's a really nice one: > > <http://www.hamware.de/hardware/tuner502/descr-at502-e.pdf> > > Get ready to sell your car and mortgage your home, however. _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
